1. Field of the Invention
The present invention relates to a high pressure fuel supply pump, in particular, applicable to a supply pump to be used in a common rail type fuel injection system for a diesel engine.
2. Description of Related Art
A conventional high pressure fuel supply pump is composed of a housing having a cylinder in which a plunger is slidably accommodated and a cylinder head in which an intake valve and a discharge valve (a check valve) are provided. According to the high pressure fuel supply pump disclosed in JP-P-2001-500593A, the cylinder head is composed of a plate in which both of the intake valve and the discharge valve are arranged and the cylinder head is attached to and fastened with the housing. This structure has a problem that fastening means for fixing the cylinder head to the housing is relatively large and complicated, since the fastening means has to endure pump chamber high pressure which the cylinder head receives, resulting in higher assembly cost and heavier body weight.
To cope with this problem, a high pressure fuel supply pump P, as shown in FIGS. 3A to 3C, is actually used. According to the high pressure fuel supply pump P, a plunger 2 is slidably accommodated in a cylinder 20 provided at a lower portion of a housing 1. An intake valve 3 is arranged at a head portion of the housing 1 coaxially with the cylinder 20 and a discharge valve 4 is arranged at a side portion of the housing 1 perpendicular to an axis of the cylinder 20. Since the intake valve 3 and the discharge valve 4 can be rigidly fixed by plugs 3A and 4A, respectively, structure of fastening the intake valve 3 and the discharge valve 4 is relatively simple and the pump P can be manufactured at less assembly cost. However, the supply pump P has a drawback in which a discharge port or conduit 18 for delivering high pressure fuel is opened to an inner circumferential wall of the cylinder 20.
In the supply pump P in which the discharge port 18 is opened to the cylinder 20 in a direction of crossing the cylinder 20, stress is concentrated to upper and lower peripheries 4C and 4D of the discharge port 18, as shown in FIG. 3B, when high pressure is applied to an inner cylindrical surface of the cylinder 20, as shown in FIG. 3C. Concentration of stress adversely affects on life time and reliability of the upper and lower peripheries 4C and 4D of the discharge port 18. Accordingly, the housing 1 has to be made of higher hardness material and, therefore, the manufacturing process is complicated, which results in higher manufacturing cost.